Amine-containing particles were characterized in an urban
area of Chongqing during both summer and winter using a single-particle
aerosol mass spectrometer (SPAMS). Among the collected particles, 12.7 %
were amine-containing in winter and 8.3 % in summer. Amines were internally
mixed with elemental carbon (EC), organic carbon (OC), sulfate, and nitrate.
Diethylamine (DEA) was the most abundant among amine-containing particles.
Wintertime amine-containing particles were mainly from the northwest
direction where a forest park was located; in summer, they were from the
northwest and southwest (traffic hub) directions. These origins suggest that
vegetation and traffic were the primary sources of particulate amines. The
average relative peak area of DEA depended strongly on humidity, indicating
that the enhancement of DEA was possibly due to increasing aerosol water
content and aerosol acidity. Using an adaptive resonance theory neural
network (ART-2a) algorithm, four major types of amine-containing particles
were clustered: amine–organic carbon (A-OC), A-OCEC, DEA-OC, and
A-OCEC aged. The identified particle types implied that amines were taken up
by particles produced from traffic and biomass burning. The knowledge gained in
this study is useful to understand the atmospheric processing, origin, and
sources of amine-containing particles in the urban area of Chongqing.

Amines are ubiquitous in the atmosphere and have both natural (ocean,
biomass burning, and vegetation) and anthropogenic (animal husbandry,
industry, combustion, and traffic) emission sources (Ge et al., 2011a).
Trimethylamine (TMA) is one of the most abundant amines with an estimated
global emission flux of 170 Gg year−1 (Ge et al., 2011a). Gaseous amines
compete with ammonia in acid–base reactions, participate in gas–particle
partitioning, and contribute to wet and dry deposition (Angelino et al.,
2001; Monks, 2005; Gómez Alvarez et al., 2007; De Haan et al., 2011;
Huang et al., 2012; You et al., 2014). Gaseous amines also play an essential
role in new particle formation by enhancing the ternary nucleation of
H2SO4–H2O clusters in remote areas (Bzdek et al., 2012;
Kirkby et al., 2011). In polluted areas, H2SO4–diethylamine–water clusters are important during new particle formation events
(Yao et al., 2018). Amines are also essential in the growth of ambient
particles. For example, particulate aminium salts, which are produced via
amine–acid neutralization, tend to prevent coagulation between
preexisting particles, leading to increased particle number concentrations
(Wang et al., 2010; Smith et al., 2010). Moreover, the enrichment of TMA has
been observed in cloud and fog processing (Zhang et al., 2012; Rehbein et
al., 2011). Characterization of amine-containing particles is important to
evaluate their processing and impact.

Single-particle mass spectrometers (SPMSs), such as an aerosol time-of-flight
mass spectrometer (ATOFMS) and single-particle aerosol mass spectrometer
(SPAMS), have been widely used in real-time measurements of amine-containing
particles for chemical composition and mixing state (Li et al., 2017). SPAMS
is different from the Aerodyne soot-particle aerosol mass spectrometer
(SP-AMS), which is a type of aerosol mass spectrometer (AMS) for detecting
black carbon, sulfate, nitrate, ammonium, chloride, and organics (Onasch et
al., 2012; Wang et al., 2016). The chemical composition and mixing state of
TMA-containing particles have been reported worldwide, such as in
California, USA (Denkenberger et al., 2007; Qin et al., 2012), Ontario,
Canada (Tan et al., 2002; Rehbein et al., 2011), Mexico City (Moffet et al.,
2008), European cities (Barcelona, Cork, Zurich, Paris, Dunkirk, and Corsica; Healy et al., 2015; Dall'Osto et al., 2016),
and Chinese cities such as
Guangzhou, Shanghai, and Xi'an (Zhang et al., 2012; Chen et al., 2016; Huang
et al., 2012). In the five European cities of Cork, Paris, Dunkirk,
Corsica, and Zurich, amines were found internally mixed with sulfate and
nitrate; but in Corsica, amines were internally mixed with methanesulfonate
(Healy et al., 2015). In Barcelona, five unique types of amine-containing
particles were observed: amine-POA58 (composed of amines, sulfate, and
nitrate), amine-EST84 (environmental tobacco smoke), amine-SOA59 (composed of TMA and
organics), amine-SOA114, and organic nitrogen amines (Dall'Osto et al., 2016, 2013). In
a rural area site in the Pearl River Delta (China), the
marker ion (C2H5)2NH2+ was the most abundant
(90 % and 86 % of amine-containing particles in summer and winter)
(Cheng et al., 2018). In Guangzhou, TMA-containing particles were important,
with up to 7 % in number fraction during clear days and 35 % during
fog events (Zhang et al., 2012). In previous studies, reported high RH
conditions and fog processing were favorable for the enhancement of
trimethylamine in the particle phase. Zhang et al. found that, during fog
events, the number fraction of TMA-containing particles was up to 35 %;
in the size range of 0.5–2.0 µm, the fraction accounted for up to 60 %
(Zhang et al., 2012). Thus, location-specific studies in varied
environments are still necessary.

Knowledge of amine-containing particles is limited in southwestern
China. In this region, Chongqing is a megacity with a population of 8.23 million. The city is subtropical, industrial, and polluted (Chen et al.,
2017; Tao et al., 2017). Fog events frequently occur in this area, and
hence it is known as the “fog city” in China. The effect of high relative
humidity (RH) on the processing of amine-containing particles needs
investigation. This study aims to characterize amine-containing
particles, including chemical composition, mixing state, atmospheric
processing, and source, in Chongqing during winter and summer.

2.1 Sampling site

Ambient single particles were collected at an urban air quality supersite
from 5 July 2016 to 8 August 2016 (referred to as a summer season) and from
21 January 2016 to 25 February 2016 (referred to as a winter season). The supersite has
been described in our previous studies (Chen et al., 2017). Briefly, the
supersite is located on the rooftop of a commercial office building
(106.51∘ E, 29.62∘ N) at a height of 30 m
above the ground (Fig. S1 in the Supplement). The building is surrounded by business and
residential communities and is 15 km from the city center. A 3 km2 forest park is located northwest of the sampling site and a traffic hub in
the southwest.

2.2 Instrumentation

A SPAMS (Hexin Inc. Guangzhou, China, model 0515) was deployed for single-particle sampling, and the technical description of SPAMS is available in
the literature (Li et al., 2011; Chen et al., 2017). Briefly, after passing
through a diffusive dryer, particles in a size range of 0.1–2.0 µm
are sampled via an aerodynamic lens and form a particle beam. Particles in
the beam come across two pre-positioned laser beams (Nd:YAG, 532 nm)
one by one, and the vacuum aerodynamic diameter (Dva) of each particle
is determined via its time of flight. Particles are ionized using an Nd:YAG
laser operating at a wavelength of 266 nm. The ions are analyzed using a
bipolar time-of-flight mass spectrometer. Due to the limitation of SPAMS,
quantification of particulate amines was not attempted.

2.3 Data analysis

The SPAMS data were imported into the YAADA toolkit (software toolkit to
analyze single-particle mass spectral data, v 2.11) to form a single-particle dataset. A query
was conducted using the marker ions of amines:
m∕z 59 [(CH3)3N]+ (TMA), 74
[(C2H5)2NH2]+ (diethylamine, DEA), 86
[(C2H5)2NCH2]+ or
[C3H7NHC2H4]+ (DEA or DPA), 101
[(C2H5)3N]+ (TEA), 102
[(C3H7)2NH2]+ (DPA), 114
[(C3H7)2NCH2]+ (DPA), and 143
[(C3H7)3N]+ (TPA) (Healy et al., 2015). Firstly, m∕z 59 was
used for querying the TMA-containing particles, followed by m∕z 74 for DEA-containing
particles, m∕z 86 for TEA-containing particles, and so on. The query
strategy resulted in duplicate particles in the results when various amines
coexisted in one single amine-containing particle. After the duplicate
particles were removed from the multiple query results described above, all
amine-containing particles were combined into an amine-containing particle
cluster. Various amines could be both internally and externally mixed in
these particle clusters.

An neural network algorithm based on adaptive resonance theory (ART-2a) was
applied to cluster the amine-containing particle types using a vigilance
factor of 0.70, a learning rate of 0.05, and 20 iterations (Song et al.,
1999). This procedure produced 67 clusters in summer and 75 clusters in
winter; many of these clusters exhibited identical mass spectra with slight
differences in specific ion intensities. A well-established combining
strategy, on the basis of similar mass spectra, temporal trends, and size
distribution, was adopted to merge these particle clusters into the
finalized particle types (Dallosto and Harrison, 2006). In addition, the
relative peak area (RPA) is defined as the peak area of each m∕z divided by
the total dual-ion mass spectral peak areas of each particle (Healy et al.,
2013). To calculate the overall RPA of amines, the relative peak areas of
amines in each particle were extracted and summed up.

3.1 Single-particle chemical composition and seasonal variation

The percentage of amine-containing particles was 12.7 % in the winter
SPAMS dataset and 8.3 % in the summer dataset. DEA-containing
particles were dominant, accounting for 70 % and 78 % of all
amine-containing particles in winter and summer, respectively; while
TMA-containing particles were minor, accounting for up to 7 % in winter
and 3 % in summer among all the amine-containing particles. The average
mass spectra of DEA-, DPA-, and TMA-containing particles are provided in
Fig. S2, and these spectra showed strong homogeneity. The determination
coefficient (R2) between DEA- and DPA-containing particles was 0.98,
and R2 between DEA- and TMA-containing particles was 0.83.

Figure 1(a, c) The positive digital mass spectrum of
amine-containing particles during summer and wintertime, respectively;
(b, d) the negative digital mass spectrum during summer and
wintertime, respectively. The ion height indicates its fraction in the
amine-containing particle dataset, and the stacked color map indicates the
ion peak area range.

Figure 1 shows the digital mass spectra of amine-containing particles in two
seasons. In each spectrum, the ion height indicates its fraction in the
amine-containing particle dataset, and the stacked color map shows the
corresponding ion intensity ranges. The assignment of ions is shown in Table S1. In both seasons, the dominant ions were K+ (m∕z 39 and 41), amines
(m∕z 59, 74, and 86), and organics (m∕z 43, 51, 63, and 77). The mixing ratios
of ammonium (NH4+, m∕z 18) and polycyclic aromatic hydrocarbons
(e.g., m∕z 116 ([C9H8]+), 129 ([C10H9]+), 140
([C11H8]+), and 153 ([C12H9]+)) were higher in
winter than in summer. The strong signal of NH4+ was possibly due
to the lower temperature (8 ∘C) in winter than in summer
(31 ∘C). The mixing ratios of m∕z 59 were 45 % and 44 % during
summer and winter, respectively.

In the negative mass spectra of two seasons (Fig. 1b and d), the
dominant ions were CN− (m∕z−26), CNO− (m∕z−42), nitrate (m∕z−46
and −62), phosphate (−79), and sulfate (m∕z−80 and −97). Primary
species, such as CN− and CNO− , were commonly from biomass burning
(BB) and organo–nitrogen (Pratt et al., 2011). Levoglucosan markers from BB,
such as −45, −59, and −71, were also detected. Dust markers, such as
[SiO2]− (m∕z−60), [28SiO3]− or
[AlO2(OH)]− (−76), and [PO3]−, were also
detected during summertime, suggesting the influence of dust particles.

Prior to comparison, the ion peak was normalized using the method developed
by Qin et al. (2012). Briefly, the peak area of each m∕z was divided by the
total mass spectral peak area matrix. The normalized ion intensity of the
wintertime particles was subtracted from that of the summertime particles. A
positive value indicates that the normalized ion intensity was greater in the
summer, whereas a negative value indicates that the normalized ion intensity
was greater in the winter. As shown in Fig. S3, Ca+ (m∕z 40) and
Fe+ (m∕z 56) were more prevalent during summer. Organic species, such as
C2H3+ (m∕z 27), C4H3+ (m∕z 51),
C5H3+ (m∕z 63), and C6H5+ (m∕z 77) typically from
aromatic hydrocarbons, were also more abundant in summer. During wintertime,
signals of sulfate (m∕z−97), NO3- (m∕z−62), NH4+
(m∕z 18), and K+ (m∕z 39) were more prominent than in summer, suggesting
that the wintertime particles contained more secondary species than those in
summer.

The unscaled size distribution of amine-containing particles also showed
strong seasonal variations (Fig. S4). Generally, amine-containing
particles had monomodal size distributions in the droplet mode, and the
distributions peaked at a larger Dva in summer than winter. For
example, DEA-containing particles peaked at 0.6 µm in winter and 0.8 µm in summer, and DPA-containing particles at 0.7 µm in winter
and 0.9 µm in summer. The size distributions of the major
amine-containing particles suggested that these particles had undergone
substantial aging processes.

Figure 2 shows the temporal tends of RH, temperature, number count, and the
peak area of amine-containing particles. The winter temperature was lower
(8.0±4.0∘C) than summer (31±4∘C), and RH in the
winter was slightly higher (70±14 % versus 64±16 %)
(Table 1). Stagnant air conditions occurred in both seasons due to low
wind speeds (Huang et al., 2017), and the winter wind speed was lower than in
summer. The hourly count of amine-containing particles was typically 10
times higher in winter than summer.

In winter, a good correlation existed between the temporal trends of hourly
number count and peak area of DEA-containing particles (R2=0.86).
The corresponding R2 in wintertime DPA-containing particles was 0.88.
No such correlation for TMA-containing particles was observed in winter
(R2=0.22) or summer (Fig. 2). The hourly counts of DEA- and
DPA-containing particles were well correlated in both summer (R2=0.63) and winter (R2=0.87), but a weak correlation (R2=0.25) existed between DEA- and TMA-containing particles. These results
suggest that DEA- and DPA-containing particles were possibly from the same
sources.

Table 1Meteorological factors and particle counts in summer and winter.

Figure 3Diurnal profiles of amine-containing particles during both
winter (a) and summer (b). The green left axis in each
panel indicates the average number count of DEA-containing particles, while
the right axis represents the number count of both DPA- and TMA-containing
particles.

Figure 4Polar plots of amine-containing particles during winter and
summertime. The axes in each figure indicate hourly count of each particle
type, and the colors within the circles represent wind speed (ws).

DEA- and DPA-containing particles remained at low levels from 20 to
26 January 2016 and averaged at 109 and 26 count h−1, respectively.
During this period, wind speed was relatively high, commonly above
1.5 m s−1. TMA-, DEA-, and DPA-containing particles started
accumulating after 26 January 2016 when wind speed was low (0.8 m s−1)
and wind direction was from the northwest. After 3 February 2016, DEA- and
DPA-containing particles showed regular diurnal patterns with high levels of
hourly count during daytime on most days and minimum levels at 15:00 local
time (UTC+8). A similar diurnal pattern was also observed for DPA-containing
particles during wintertime (Fig. 3). TMA-containing particles presented a
complex diurnal profile with peaks in the early morning (04:00), at noon
(12:00), and in the afternoon (18:00). The chemical composition and diurnal
pattern of TMA-containing particles were strongly connected to traffic
emissions.

Wind direction and the number count of amine-containing particles were analyzed
together using bivariate polar plots (Fig. 4). During wintertime, the
dominant direction for amine-containing particles was from the northwest
where a forest park was located. After being emitted from vegetation
(plants, grass, and trees) (Ge et al., 2011a), DEA could partition to
preexisting particles before arriving at the sampling site. The transport
of these particles to the sampling site caused the elevation in the morning.
Based on the excellent correlation between DEA- and DPA-containing
particles, DPA-containing particles could also be from vegetation. It can be
concluded that the major source of amines in DEA- and DPA-containing
particles was vegetation from the northwest.

During summer, amine particles appeared in several episodes; each
episode lasted for 1–3 days. In these episodes,
DPA-containing particles had two rush-hour peaks (07:00 and 17:00), likely
from traffic (Dall'Osto et al., 2016). Besides traffic, vegetation is also a
source of DPA-containing particles (from the southwest; Fig. 4e). The
DPA-containing particles peaked 0.84 µm, suggesting that they were not
freshly emitted and had undergone substantial aging processes. Moreover, as
shown in Fig. S2, the mass spectra of the amines were present with
aromatic hydrocarbon fragments, such as
C4H3+ (m∕z 51),
C5H3+ (m∕z 63),
C6H5+ (m∕z 77), and
C9H8+ (m∕z 116), as well as with alkane fragments such as
C4H7+ (m∕z 55),
C4H9+ (m∕z 57), and
C5H9+ (m∕z 69). The chemical composition of DPA-containing
particles contained markers associated with traffic emissions. A similar
amine-containing particle type has been reported in the literature
(Dall'Osto et al., 2016).

In summer, DEA-containing particles had a diurnal pattern of three peaks
appearing at 03:00, 09:00, and 17:00. TMA-containing particles had an early
morning (04:00) and a noon peak (12:00). The morning peaks of DEA- and
TMA-containing particles could be due to local traffic emissions;
specifically, heavy-duty vehicles were only allowed to enter the urban area
between 00:00 and 06:00 (Chen et al., 2017). The polar plots showed that
DEA-containing particles were from the northwest and southwest, passing
through the forest park and traffic hub, respectively. This scenario seemed
to be inconsistent with the wintertime results because of the limited
traffic contributions to particle levels in winter. In addition, due to the
competition between vegetation and traffic in summer, the number count and
peak area of all three amine-containing particles were poorly correlated
with each other.

3.3 Effect of RH on the enrichment of DEA-containing particles

DEA-containing particles were predominant in both winter and summer,
providing a unique opportunity for investigating DEA processing. Indeed, the
effect of RH on aerosol chemical processing should be treated cautiously and
the influences of wind speed, wind direction, temperature, and planetary
boundary layer reduction should be removed. As described above, the average
wind speed in winter and summer was 1.2 and 1.5 m s−1,
respectively. In these stagnant air conditions, the sampled particles were
generally local. Temperature could influence gas–particle phase
partitioning. Assuming that the Henry's law constants (KH) and the enthalpy
change ΔrHo(KH) of DEA are constant, a variation of
10 ∘C in both summer and winter has a negligible influence on
the partitioning of amines from the gas phase to the particle phase,
according to the Clapeyron equation (Ge et al., 2011b). In addition, the
shift in planetary boundary layer (PBL) height could affect the number count
and concentration of PM. Using the temporal trends of RPA, the influence of
PBL height can be removed because it only shows the relative changes between
different species, which are all simultaneously influenced by the shift in
the PBL height.

Box plots of DEA relative peak area under different RH are shown in Fig. 5.
In winter, the median RPA of amine-containing particles increased by 2
times when RH increased from 35 % to 95 %. Meanwhile, the fraction of
DEA-containing particles increased from 4.0 % to 16.6 %. In summer,
the average RPA of DEA increased by 3 times (from 0.25 to 0.75), and the
fraction of DEA-containing particles increased from 3.8 % to 12.1 % when
RH increased from 60 % to 90 %. These results suggest that RH is
important to the enrichment of DEA in the particle phase. When DEA reacts
with HCl, H2SO4, and HNO3, it tends to form aminium
salts, which are soluble in aerosol water. Along with the influence of
aerosol water content, Ge et al. (2011a) also proposed that strong aerosol
acidity could enhance the partitioning of DEA in the aqueous phase. As
particles are dried in the SPAMS, the amounts of aerosol water content and pH
were unavailable. Values of the anion-to-cation ratio
((sulfate + nitrate) ∕ ammonium; Yao et al., 2011) were in a range of
20–150, suggesting that the particles might have been acidic, which favors the
dissolution of DEA. Overall, these results implied that high RH conditions in
Chongqing were favorable for particle uptake of DEA, and the resulting
formation of aminium salts stabilized preexisting particles, thus increasing
their number concentrations.

Figure 5Box plots of the hourly relative peak area of DEA under different RH
conditions in winter (a) and summer (b). The boxes indicate
the 25th and 75th percentiles; the dots indicate mean value with each data
point representing a datum of RPA in an hour size bin. Right axis in each
panel and the blue diamonds show the average number fraction of
amine-containing particles among the whole SPAMS dataset.

Rehbein et al. (2011) and Zhang et al. (2012) observed direct links between
fog processing and enhancement of TMA-containing particles. High RH
conditions were favorable for TMA entering the particle phase via gas–particle partitioning (Rehbein et al., 2011; Zhang et al., 2012). Ge et al. (2011b) argued that TMA in the aerosol phase was in the form of free base,
e.g., amine, not aminium salt; TMA could be dissolved in aerosol water
and
the formation of TMA–HSO4 salt was possible, but the formation of
TMA–NO3 and TMA–Cl was impossible due to competition with ammonia.
Thus, TMA could enter the aerosol phase by gas–aqueous partitioning or in
the form of TMA–HSO4 salt. The mechanism of DEA entering the aerosol
phase might be different from TMA. DEA salts were favorable for forming in
the
aerosol phase (Ge et al., 2011b). Pankow (2015) proposed that the
absorptive uptake of atmospheric amines could also be possible on organic
aerosols. In the context of single-particle mixing state, the
amine-containing particles were internally mixed with hygroscopic species,
e.g., sulfate, nitrate, POA species (CxHy+; see Sect. 3.4),
and SOA species (oxalate, C2H3O+). Therefore, the mixing
state of amine-containing particles was also favorable for the uptake of
amines via different pathways: the aqueous dissolution of aminium salts and
absorptive uptake on OA.

3.4 Particle types of amine-containing particles

As shown in Fig. 6, four amine-containing particle types were resolved,
including amine–OC (A-OC, 41 %), A-ECOC (39 %), DEA-OC (11 %), and
A-ECOC aged (9 %). All of these particle types had strong signals of
amines, and the amines were internally mixed with sulfate, nitrate,
elemental carbon, and organics.

In the A-OC particles, amines were mixed with aromatic hydrocarbon
fragments, such as
C4H3+ (m∕z 51),
C5H3+ (m∕z 63),
C6H5+ (m∕z 77), and
C9H8+ (m∕z 116), as
well as with alkanes fragments such as
C4H7+ (m∕z 55),
C4H9+ (m∕z 57), and
C5H9+ (m∕z 69). In the
negative mass spectrum of A-OC, strong signals from CN− (m∕z−26) and
CNO− (m∕z−42) were typically primary species, along with levoglucosan
(Silva et al., 1999). The amine fragments, such as TMA (m∕z 59), DEA (m∕z 74),
and DPA (m∕z 86), were very abundant in this particle type (76 %, 95 %,
and 88 %, respectively). The parent particles of A-OC were a kind of OC
particle from biomass burning; then they mixed with amines via uptake.
Amines could enter the A-OC particle type via dissolution in the aerosol
water content or uptake due to absorptive uptake on the organic aerosol
(Pankow, 2015).

In A-ECOC mass spectra, strong signals of amines (m∕z 59 and 74), along with
the major aromatic hydrocarbon fragments and EC components (i.e., m∕z 36, 48,
60), were detected. In the negative mass spectra, nitrate and sulfate were
also dominant. The A-ECOC aged particle type had a similar chemical
composition to A-ECOC (R2=0.53) but with weaker relative intensities
of CxHy+ and amine ions, suggesting it could be more
secondary.

In the positive mass spectra of DEA-OC, the DEA fragment (m∕z 74) was dominant and
present with the organic fragments described above. Secondary organic marker
ions, such as m∕z 43 ([C2H3O]+) and −89 (oxalic acid), were
found in the mass spectra. DEA-OC was not sensitive to wind speed
(R2=0.18), implying they were local.

The summertime amine-containing particles were similar to the particle types
during winter (all R2>0.7), except that a Ca-rich particle type
was also resolved (Fig. S5). The A-Ca-OC particle type was mainly composed of
calcium (Ca+ and CaO+), sodium (m∕z 23), potassium (m∕z 39), TMA
(m∕z 59), sulfate, nitrate, and phosphate. An ion signal of zinc (m∕z 64) was
observed in the positive mass spectrum. Zn is a marker for tire wear on
roads (Grigoratos and Martini, 2015; Thorpe and Harrison, 2008). The A-Ca-OC
particle type was possibly from traffic activities (Chen et al., 2017).

The amine-containing particle types reported in this study are different
from those in the literature. Cheng et al. (2018) reported that m∕z 74
amine-containing particles were most abundant in the Pearl River Delta,
China, but the chemical composition and mixing state of amine particles were
different from this study. For example, the mixing ratio of DPA was much
stronger (∼0.2) in Guangdong than in Chongqing (<0.1). In most related studies, TMA-containing particles were dominant, while
the present study shows that DEA-containing particles were dominant (Rehbein et
al., 2011; Zhang et al., 2012; Healy et al., 2015; Dall'Osto et al., 2016).

Amine-containing particles were collected and analyzed during winter and
summer in the urban area of Chongqing. Generally, amine-containing particles
were more abundant in winter than in summer. DEA-containing particles
(m∕z 74) were the most important particle type during both summer and winter.
Amines were internally mixed with EC components, organics, sulfate, and
nitrate, suggesting that particle aging was significant in both seasons.
Amine-containing particles had monomodal size distributions in the droplet
mode, and the distributions peaked at a larger Dva in summer than
winter. DEA- and DPA-containing particles showed strong homogeneity, and
good correlations between the hourly number count and peak area were
observed during winter. The amine-containing particles were mostly from
vegetation located southwest of the sampling area and traffic sources in
the northwest. An enrichment of DEA-containing particles under high RH
conditions was revealed. Reduction of anthropogenic amines, such as DEA and
TMA, would improve the air quality in this region, which can be achieved by
decreasing the emissions of on-road fuel-powered automobiles.

Financial support from the National Key Research and Development Program of
China (2018YFC0200403 and 2016YFC0200405), the Nature Science Foundation of
China (grant no. 41375123), and the Educational Commission of Sichuan
Province of China (no. 15ZA0213) is acknowledged.

Amine-containing particles were characterized in an urban area of Chongqing during both summer and winter using a single-particle aerosol mass spectrometer (SPAMS). Amines were observed to internally mix with elemental carbon (EC), organic carbon (OC), sulfate, and nitrate. Diethylamine (DEA) was the most abundant in both number and peak area among amine-containing particles. Vegetation and traffic were the primary sources of particulate amines.

Amine-containing particles were characterized in an urban area of Chongqing during both summer...